Synthesis of α,β-alkynyl ketones via the nickel catalysed carbonylative Sonogashira reaction using oxalic acid as a sustainable C1 source

Oxalic acid as a dual C1 surrogate for heterogeneous palladium-catalyzed tandem four-component quinazolinone synthesis

Herein, a heterogeneous Pd/C-catalyzed direct one-step four-component double carbonylative approach for cascade synthesis of 2-aryl quinazolinones has been reported for the first time starting from 2-iodoaniline derivatives and aryl iodides. The given reaction involves the simultaneous implementation of two different gaseous surrogates i.e., ammonium carbamate as an NH3 precursor and oxalic acid as a bi-functional reagent acting as a CO as well as a C-atom surrogate under ligand-free conditions.

Recent advances in the application of alkynes in multicomponent reactions

Alkynes have two active positions to carry out chemical reactions: C[triple bond, length as m-dash]C and C-H. These two positions are involved and activated in different reactions using different reagents. In this study, we investigated the reactions of alkynes that are involved in multi-component reactions through the C-C and C-H positions and examined the progress and gaps of each reaction by carefully studying the mechanism of the reactions. Firstly, we investigated and analyzed the reactions involving the C[triple bond, length as m-dash]C position of alkynes, including the reactions between derivatives of alkynes with RN3, sulfur compounds (RSO2R', DMSO, S8, DABCO(SO2)2 and DABSO), barbituric acids, aldehydes and amines, COOH, α-diazoesters or ketones, and isocyanides. Then, we examined and analyzed the important reactions involving the C-H position of alkynes and the progress and gaps in these reactions, including the reaction between alkyne derivatives with amines and aldehydes for the synthesis of propargylamines, the reaction between alkynes with CO2 and the reaction between alkynes with CO.

Palladium-Catalyzed Aminocarbonylation of Isoquinolines Utilizing Chloroform-COware Chemistry

The carbonyl group forms an integral part of several drug molecules and materials; hence, synthesis of carbonylated compounds remains an intriguing area of research for synthetic and medicinal chemists. Handling toxic CO gas has several limitations; thus, using safe and effective techniques for in or ex situ generation of carbon monoxide from nontoxic and cheap precursors is highly desirable. Among several precursors that have been explored for the generation of CO gas, chloroform can prove to be a promising CO surrogate due to its cost-effectiveness and ready availability. However, the one-pot chloroform-based carbonylation reaction requires strong basic conditions for hydrolysis of chloroform that may affect functional group tolerability of substrates and scale-up reactions. These limitations can be overcome by a two-chamber reactor (COware) that can be utilized for ex situ CO generation through hydrolysis of chloroform in one chamber and facilitating safe carbonylation reactions in another chamber under mild conditions. The versatility of this "Chloroform-COware" technique is explored through palladium-catalyzed aminocarbonylation of medicinally relevant heterocyclic cores, viz., isoquinoline and quinoline.

Nickel catalysts in Sonogashira coupling reactions

Nickel has emerged as a desirable substitute for palladium in Sonogashira coupling reactions due to its abundance, less toxicity and high catalytic activity. Ni complexes have been developed to catalyse C(sp)-C(sp2) and C(sp)-C(sp3) Sonogashira couplings that find applications in the synthesis and modifications of biologically relevant molecules. This review focuses on the catalytic potential and mechanistic details of various Ni complexes employed in the Sonogashira coupling. These include homogeneous catalytic systems with Ni-phosphorus and Ni-nitrogen catalysts, ligand-free catalysts, and carbonylative coupling strategies. Various heterogeneous catalytic systems using supported Ni complexes, Ni nanoparticles and Pd-Ni bimetallic catalysts have also been discussed. This is the first review reported so far dealing exclusively with Ni-catalysed Sonogashira coupling reactions. This review illustrates the current strategies and potential of Ni-catalysed Sonogashira coupling reactions in both homogeneous and heterogeneous systems, and covers the literature up to 2020.

Palladium-catalyzed [2 + 2 + 1] annulation: access to chromone fused cyclopentanones with cyclopropenone as the CO source

A variety of chromone fused cyclopentanones are efficiently generated in good to high yields via palladium-catalyzed [2 + 2 + 1] annulation, in which cyclopropenone was utilized for the first time as the sole CO surrogate in the carbonylation process.

Supported palladium catalyzed aminocarbonylation of aryl iodides employing bench-stable CO and NH3 surrogates

A simple, efficient and phosphine free protocol for carbonylative synthesis of primary aromatic amides under polystyrene supported palladium (Pd@PS) nanoparticle (NP) catalyzed conditions has been demonstrated. Herein, instead of using two toxic and difficult to handle gases simultaneously, we have employed the solid, economical, bench stable oxalic acid as the CO source and ammonium carbamate as the NH3 source in a single pot reaction. For the first time, we have applied two non-gaseous surrogates simultaneously under heterogeneous catalyst (Pd@PS) conditions for the synthesis of primary amides using an easy to handle double-vial (DV) system. The developed strategy showed a good functional group tolerance towards a wide range of aryl iodides and afforded primary aromatic amides in good yields. The Pd@PS catalyst was easy to separate and can be recycled up to four consecutive runs with small loss in catalytic activity. We have successfully extended the scope of the methodology to the synthesis of isoindole-1,3-diones from 1,2-dihalobenzene, 2-halobenzoates and 2-halobenzoic acid following double and single carbonylative cyclization approaches.

Palladium-catalyzed ortho-halogen-induced deoxygenative approach of alkyl aryl ketones to 2-vinylbenzoic acids

The 2-vinylbenzoic acids have wide applications in the field of polymer chemistry and are key precursors for the synthesis of important bioactive molecules. Herein, an ortho-halogen-induced deoxygenative approach for the generation of 2-vinylbenzoic acids from alkyl aryl ketones by palladium catalysis is discovered and explored. This approach requires no base or stoichiometric additives and can be carried out through a simple one-step process. Furthermore, the present reaction is scalable up to one-gram scale. The commercially available palladium on carbon (5 wt%) was used as a heterogeneous catalyst and showed excellent recyclability (<5 times) without significant loss in catalytic activity. Pleasingly, under our optimized conditions, the alpha alkyl substituted 2-iodoacetophenones exhibit good diastereoselectivity and predominantly (E)-2-vinylbenzoic acids were obtained with good to excellent yields.

Nickel-catalyzed allylic carbonylative coupling of alkyl zinc reagents with tert-butyl isocyanide

Transition metal-catalyzed carbonylation with carbon nucleophiles is one of the most prominent methods to construct ketones, which are highly versatile motifs prevalent in a variety of organic compounds. In comparison to the well-established palladium catalytic system, the nickel-catalyzed carbonylative coupling is much underdeveloped due to the strong binding affinity of CO to nickel. By leveraging easily accessible tert-butyl isocyanide as the CO surrogate, we present a nickel-catalyzed allylic carbonylative coupling with alkyl zinc reagent, allowing for the practical and straightforward preparation of synthetically important β,γ-unsaturated ketones in a linear-selective fashion with excellent trans-selectivity under mild conditions. Moreover, the undesired polycarbonylation process which is often encountered in palladium chemistry could be completely suppressed. This nickel-based method features excellent functional group tolerance, even including the active aryl iodide functionality to allow the orthogonal derivatization of β,γ-unsaturated ketones. Preliminary mechanistic studies suggest that the reaction proceeds via a π-allylnickel intermediate.

In contrast to the well-established palladium-catalyzed version, the nickel-catalyzed carbonylative coupling is underdeveloped. Here the authors report a nickel-catalyzed allylic carbonylative coupling with alkyl zinc reagents, allowing for preparation of β,γ-unsaturated ketones in a linear-selective fashion.